Module scope in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable inside a module scope.

Javascript

const [1] = 10;
console.log(value);

Drag options to blanks, or click blank then click option'

AvarValue

BmoduleVar

Cvalue

DglobalValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name than the one logged.

Using var which is function scoped, not module scoped.

The variable value is declared with const inside the module, so it is scoped to this module only.

2fill in blank

medium

Complete the code to export a function from a module.

Javascript

export default function [1]() {
  return 'Hello from module';
}

Drag options to blanks, or click blank then click option'

AsayHello

Bgreet

ChelloWorld

Dwelcome

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name that is not descriptive.

Forgetting to export the function.

The function greet is exported so it can be used outside this module.

3fill in blank

hard

Fix the error in the code by completing the import statement correctly.

Javascript

import [1] from './module.js';
console.log(greet());

Drag options to blanks, or click blank then click option'

Agreet

BsayHello

Chello

Dwelcome

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different name than the exported function.

Forgetting to import the function.

The import must match the exported function name greet from the module.

4fill in blank

hard

Fill both blanks to create a private variable and a public function accessing it.

Javascript

const [1] = 42;
export function getValue() {
  return [2];
}

Drag options to blanks, or click blank then click option'

AsecretNumber

BsecretValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names in the two blanks.

Trying to export the variable directly.

The variable secretNumber is private to the module, and the exported function getValue returns its value.

5fill in blank

hard

Fill all three blanks to export a constant, import it, and log its value.

Javascript

export const [1] = 3.14;

import { [2] } from './constants.js';

console.log([3]);

Drag options to blanks, or click blank then click option'

API

DE

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for export and import.

Logging a variable that was not imported.

The constant PI is exported, imported, and logged correctly.

Practice

1. What does module scope mean in JavaScript?

easy

A. All variables are global and accessible everywhere

B. Variables and functions are private to the file unless exported

C. Functions can only be used inside loops

D. Variables must be declared with var only

Solution

1. Step 1: Understand module scope concept

   Module scope means code inside a file is private unless explicitly shared.

2. Step 2: Compare options with this concept

   Only Variables and functions are private to the file unless exported correctly states variables/functions are private unless exported.

3. Final Answer:

   Variables and functions are private to the file unless exported -> Option B

4. Quick Check:

   Module scope = private unless exported [OK]

Hint: Remember: module code is private unless exported [OK]

Common Mistakes:

• Thinking all variables are global
• Confusing module scope with block scope
• Believing functions must be inside loops

2. Which of the following is the correct way to export a function named greet from a module?

easy

A. export function greet() {}

B. function export greet() {}

C. export greet() {}

D. export = greet()

Solution

1. Step 1: Recall correct export syntax

   To export a function, use export function functionName() {}.

2. Step 2: Check each option

   export function greet() {} matches the correct syntax; others are invalid or incorrect.

3. Final Answer:

   export function greet() {} -> Option A

4. Quick Check:

   Export function syntax = export function name() [OK]

Hint: Use 'export function' before function name [OK]

Common Mistakes:

• Placing export after function keyword
• Using incorrect export assignment syntax
• Missing parentheses in function declaration

3. Given this module code:

const secret = 42;
export const visible = 'hello';

console.log(typeof secret);
console.log(typeof visible);

What is the output when this module runs?

medium

A. "number" and "string"

B. "undefined" and "string"

C. "number" and "undefined"

D. ReferenceError for secret

Solution

1. Step 1: Understand variable scope and export

   Both secret and visible exist inside the module; secret is private, visible is exported.

2. Step 2: Check typeof outputs inside the same module

   Inside the module, both variables exist, so typeof secret is "number" and typeof visible is "string".

3. Final Answer:

   "number" and "string" -> Option A

4. Quick Check:

   typeof secret = number, typeof visible = string [OK]

Hint: Inside module, all declared variables exist [OK]

Common Mistakes:

• Thinking private variables are undefined inside module
• Confusing export with variable existence
• Expecting ReferenceError inside same file

4. What is wrong with this module code?

const count = 10;
export count = 20;

medium

A. Cannot export a variable twice

B. count is not declared before export

C. Syntax error: export cannot be used with assignment

D. No error, code works fine

Solution

1. Step 1: Analyze export syntax

   Export keyword cannot be used with assignment like export count = 20;. It must be export const count = 20; or export existing variables.

2. Step 2: Identify error type

   This causes a syntax error because export expects declaration or named export, not assignment.

3. Final Answer:

   Syntax error: export cannot be used with assignment -> Option C

4. Quick Check:

   Export syntax must declare or export existing variables [OK]

Hint: Export must declare or export, not assign [OK]

Common Mistakes:

• Trying to export by assignment
• Missing const/let/var with export
• Assuming export can change variable value

5. You have two modules:

// file1.js
const secret = 'hidden';
export const data = 123;

// file2.js
import { data } from './file1.js';
console.log(secret);
console.log(data);

What will happen when file2.js runs?

hard

A. Logs undefined and 123

B. Logs 'hidden' and 123

C. SyntaxError due to import

D. ReferenceError: secret is not defined

Solution

1. Step 1: Understand module scope and imports

   The variable secret is private to file1.js and not exported, so it cannot be accessed in file2.js.

2. Step 2: Predict runtime behavior

   Trying to access secret in file2.js causes a ReferenceError. The imported data logs correctly.

3. Final Answer:

   ReferenceError: secret is not defined -> Option D

4. Quick Check:

   Private variables cause ReferenceError outside module [OK]

Hint: Only exported variables are accessible in other modules [OK]

Common Mistakes:

• Assuming private variables are imported automatically
• Confusing import syntax errors with runtime errors
• Expecting undefined instead of ReferenceError